The present invention relates to an overcharge prevention method, which is suitable for preventing overcharging, a charging circuit, electronic equipment which uses the overcharge prevention method and the charging circuit, and a timepiece.
A diode bridge circuit is well known as a charging circuit that charges a large-capacity capacitor with an alternating voltage generated by a generator. In the diode bridge circuit, since losses for only two diode voltage drops are generated, it is not suitable for charging small amplitude alternating voltage.
Accordingly, a charging circuit which uses a transistor instead of diodes has been developed. For example, FIG. 15 is a circuit diagram of a conventional charging circuit. In this charging circuit, there are provided comparators COM1 and COM2 for comparing the voltages at output terminals A and B, respectively, of a generator AG with the power supply voltage Vdd, comparators COM3 and COM4 for comparing the voltages at the output terminals A and B, respectively, of the generator AG with the ground voltage GND, and a large-capacity capacitor C for storing a charging current. Then, switching ON/OFF of P-channel FETs P1 and P2 and N-channel FETs N1 and N2 is controlled according to the outputs of the respective comparators COM1 to COM4.
Herein, when the voltage at the output terminal A becomes equal to or less than the ground voltage GND, the N-channel FET N1 is turned ON by the comparator COM3, and the output terminal A is grounded. Further, when the voltage of the output terminal B exceeds the power supply voltage Vdd, the P-channel FET P2 is turned ON by the comparator COM2, and electrical charge flows into the capacitor C through a path indicated with the arrow. In this case, unless the voltage of the output terminal B exceeds the power supply voltage Vdd, the P-channel FET P2 will not turn ON, and it is arranged to prevent any problems from occurring such as a current flowing through a path opposite to the arrow, thereby deteriorating the charging efficiency.
Incidentally, in the charging circuit as described above, since switching ON/OFF of the respective field effect transistors (FETs) is controlled by the comparators COM1 to COM4, the configuration becomes complex, and the scale of the circuit and a current consumption increases.
On the other hand, there is a breakdown voltage for the large-capacity capacitor, and when the charging voltage exceeds a predetermined voltage, overcharging occurs, the large-capacity capacitor is degraded, and the charging efficiency drops.
It is an object of the present invention to provide an overcharge prevention method, which is capable of securely preventing overcharging with a simple configuration, and a charging circuit which is capable of securely preventing overcharging.
It is another object of the present invention to apply this charging circuit to electronic devices and a wristwatch.
The present invention is characterized in that an overcharge prevention method, which is adapted to be used in a charging circuit for charging electrical power into a charging element, using a rectifying circuit having a plurality of rectifying elements, which converts an alternating-current input from an external alternating-current power supply through a pair of input terminals to a direct-current and outputs the direct-current, characterized in that the method comprises the steps of detecting a charging voltage of the charging element; and shunting the pair of input terminals without passing through the plurality of rectifying elements when the detected charging voltage exceeds a predetermined voltage that is defined in advance.
Further, the present invention is characterized in that an overcharge prevention method, which is adapted to be used in a charging circuit for charging electrical power into a charging element, using a rectifying circuit having a plurality of rectifying elements, which converts an alternating current input from an external alternating-current power supply through a pair of input terminals to a direct current and outputs the direct current, characterized in that the method comprises the steps of detecting a charging voltage of the charging element; comparing the detected charging voltage with a reference voltage that is defined in advance; and shunting the pair of input terminals without passing through the plurality of rectifying elements when the detected charging voltage exceeds the reference voltage.
Further, the present invention is characterized in that an overcharge prevention method which is used in a charging circuit, the charging circuit comprising first and second switching means with which it is controlled whether or not, according to a terminal voltage at one of the input terminals to which an alternating-current voltage is supplied, the other one of the input terminals and a first power supply line are connected, first and second diodes which are connected between the respective input terminals and a second power supply line, and a charging element for rectifying the alternating-current voltage and for charging electrical power into the charging element, characterized in that the method comprises the steps of detecting a charging voltage of the charging element; comparing the detected charging voltage with a reference voltage that is defined in advance; and supplying a generator current that flows into one of the input terminals to the other one of the input terminals through a path that does not pass through the first and second diodes when the detected charging voltage exceeds the reference voltage.
Further, the present invention is characterized in that a generator current that flows into one of the input terminals is supplied to the other one of the input terminals through a path that does not pass through the first and second diodes by shunting both of the input terminals, when the detected charging voltage exceeds the reference voltage.
Moreover, the present invention is characterized in that a charging circuit for charging electrical power into a charging element, using a rectifying circuit having a plurality of rectifying elements, which converts an alternating-current input from an external alternating-current power supply through a pair of input terminals to a direct current and outputs the direct current, characterized in that the charging circuit comprises charging voltage detecting means for detecting a charging voltage of the charging element; and shunt means for shunting the pair of input terminals without passing through the plurality of rectifying elements when the detected charging voltage exceeds a predetermined voltage that is defined in advance.
Furthermore, the present invention is characterized in that a charging circuit for charging electrical power into a charging element, using a rectifying circuit having a plurality of rectifying elements, which converts an alternating current input from an external alternating-current power supply through a pair of input terminals to a direct current and outputs the direct current, characterized in that the charging circuit comprises charging voltage detecting means for detecting a charging voltage of the charging element; comparison means for comparing the detected charging voltage with a reference voltage that is defined in advance; and shunt means for shunting the pair of input terminals without passing through the plurality of rectifying elements when the detected charging voltage exceeds the reference voltage.
The present invention is further characterized in that a charging circuit for rectifying an alternating-current voltage supplied to first and second input terminals and for charging an electrical charge into a charging element that is provided between first and second power supply lines, comprising first switching means provided between the first input terminal and the first power supply line, in which ON/OFF switching thereof is controlled on the basis of a voltage at the second input terminal; second switching means provided between the second input terminal and the first power supply line, in which ON/OFF switching thereof is controlled on a basis of a voltage at the first input terminal; a first diode provided between the first input terminal and the second power supply line; a second diode provided between the second input terminal and the second power supply line; comparison means for detecting a charging voltage of the charging element, and for comparing the detected charging voltage with a reference voltage that is defined in advance; and shunt means for shunting the first input terminal and the second input terminal by supplying a generator current that is flown into one of the input terminals to the other one of the input terminals through a path that does not pass through the first and second diodes, based on a comparison result in the comparison means.
Further, the present invention is characterized in that the shunt means is a transistor provided between the first input terminal and the second input terminal.
The present invention is further characterized in that the shunt means comprises a third diode in which one end thereof is connected to the first input terminal; a fourth diode in which one end thereof is connected to the second input terminal; and a transistor which is connected to the other ends of the third and fourth diodes and is also connected to the first and second power source lines.
The present invention is further characterized in that a charging circuit for rectifying an alternating-current voltage supplied to first and second input terminals and for charging electrical power into a charging element that is provided between a high-potential power supply line and a low-potential power supply line, comprising a first diode in which an anode thereof is connected to the first input terminal, and a cathode thereof is connected to the high-potential power supply line; a second diode in which an anode thereof is connected to the second input terminal, and a cathode thereof is connected to the high-potential power supply line; a first N-channel field effect transistor in which a drain thereof is connected to the first input terminal, a source thereof is connected to the low-potential power supply line, and a gate thereof is connected to the second input terminal; a second N-channel field effect transistor in which a drain thereof is connected to the second input terminal, a source thereof is connected to the low-potential power supply line, and a gate thereof is connected to the first input terminal; a comparator for comparing a charging voltage of the charging element with a reference voltage that is defined in advance, and a transmission gate provided between the first and second input terminals, in which ON/OFF switching thereof is controlled on the basis of a comparison result of the comparator.
The present invention is further characterized in that a charging circuit for rectifying an alternating-current voltage supplied to first and second input terminals and for charging electrical power into a charging element that is provided between a high-potential power supply line and a low-potential power supply line, comprising a first diode in which a cathode thereof is connected to the first input terminal, and an anode thereof is connected to the low-potential power supply line; a second diode in which a cathode thereof is connected to the second input terminal, and an anode thereof is connected to the low-potential power supply line; a first P-channel field effect transistor in which a drain thereof is connected to the first input terminal, a source thereof is connected to the high-potential power supply line, and a gate thereof is connected to the second input terminal; a second P-channel field effect transistor in which a drain thereof is connected to the second input terminal, a source thereof is connected to the high-potential power supply line, and a gate thereof is connected to the first input terminal; a comparator for comparing a charging voltage of the charging element with a reference voltage that is defined in advance, and a transmission gate provided between the first and second input terminals, in which ON/OFF switching thereof is controlled on a basis of a comparison result of the comparator.
Further, the present invention is characterized in that a charging circuit for rectifying an alternating-current voltage supplied to first and second input terminals and for charging electrical power into a charging element that is provided between a high-potential power supply line a low-potential power supply line, comprising a first diode in which an anode thereof is connected to the first input terminal, and a cathode thereof is connected to the high-potential power supply line; a second diode in which an anode thereof is connected to the second input terminal, and a cathode thereof is connected to the high-potential power supply line; a first N-channel field effect transistor in which a drain thereof is connected to the first input terminal, a source thereof is connected to the low-potential power supply line, and a gate thereof is connected to the second input terminal; a second N-channel field effect transistor in which a drain thereof is connected to the second input terminal, a source thereof is connected to the low-potential power supply line, and a gate thereof is connected to the first input terminal; a comparator for comparing a charging voltage of the charging element with a reference voltage that is defined in advance; a third diode in which an anode thereof is connected to the first input terminal; a fourth diode in which an anode thereof is connected to the second input terminal; and a third N-channel field effect transistor in which a drain thereof is connected to cathodes of the third and fourth diodes, a source thereof is connected to the low-potential power supply line, and a comparison result of the comparator is supplied to a gate thereof.
Moreover, the present invention is characterized in that a charging circuit for rectifying an alternating-current voltage supplied to first and second input terminals and for charging electrical power into a charging element that is provided between a high-potential power supply line and a low-potential power supply line, comprising a first diode in which a cathode thereof is connected to the first input terminal, and an anode thereof is connected to the low-potential power supply line; a second diode in which a cathode thereof is connected to the second input terminal, and an anode thereof is connected to the low-potential power supply line; a first P-channel field effect transistor in which a drain thereof is connected to the first input terminal, a source thereof is connected to the high-potential power supply line, and a gate thereof is connected to the second input terminal; a second P-channel field effect transistor in which a drain thereof is connected to the second input terminal, a source thereof is connected to the high-potential power supply line, and a gate thereof is connected to the first input terminal; a comparator for comparing a charging voltage of the charging element with a reference voltage that is defined in advance; a third diode in which a cathode thereof is connected to the first input terminal; a fourth diode in which a cathode thereof is connected to the second input terminal; and a third P-channel field effect transistor in which a drain thereof is connected to anodes of the third and fourth diodes, a source thereof is connected to the high-potential power supply line, and a comparison result of the comparator is supplied to a gate thereof.
The present invention is further characterized in that a charging circuit for rectifying an alternating-current voltage supplied to first and second input terminals and for charging electrical power into a charging element that is provided between a high-potential power supply line and a low-potential power supply line, comprising a first diode in which an anode thereof is connected to the first input terminal, and a cathode thereof is connected to the high-potential power supply line; a second diode in which an anode thereof is connected to the second input terminal, and a cathode thereof is connected to the high-potential power supply line; a first N-channel field effect transistor in which a drain thereof is connected to the first input terminal, a source thereof is connected to the low-potential power supply line, and a gate thereof is connected to the second input terminal; a second N-channel field effect transistor in which a drain thereof is connected to the second input terminal, a source thereof is connected to the low-potential power supply line, and a gate thereof is connected to the first input terminal; a comparator for comparing a charging voltage of the charging element with a reference voltage that is defined in advance; a third N-channel field effect transistor in which a drain thereof is connected to the first input terminal, a source thereof is connected to the low-potential power supply line, and a gate thereof is connected to an output terminal of the comparator; and a fourth N-channel field effect transistor in which a drain thereof is connected to the second input terminal, a source thereof is connected to the low-potential power supply line, and a gate thereof is connected to an output terminal of the comparator.
An electronic equipment of the present invention is characterized in that there is installed a charging circuit according to the respective embodiments described above and operates in accordance with electrical power that is supplied from the charging circuit.
A timepiece of the present invention is characterized in that there is installed a charging circuit according to the respective embodiments described above and includes a clock circuit that measures time in accordance with electrical power that is supplied from the charging circuit.